Pressure-actuated valve with metering choke

ABSTRACT

A metering apparatus for controlling the rate of closure of a pressure-actuated valve of a type normally used in irrigation systems. When a pressure-actuated valve is closing, fluid from a supply line must flow into a pressure-actuating chamber, gradually filling it to force the valve&#39;s plug member against its seat. The metering apparatus is a compressible spring through which fluid must flow to enter this pressure-actuating chamber. As the valve closes, it compresses the spring through which the fluid must flow, thereby restricting the rate of flow into the pressure-actuating chamber. This reduction in flow reduces the rate at which the valve&#39;s plug member approaches its seat in an exponential manner, allowing rapid closure at first which is reduced considerably as the plug approaches its seat. Such a restricted closure rate prevents pressure shock in the supply line, otherwise known as hammering or chatter, which causes damage and excess wear and tear to the supply line, to the pressure-actuated valve and to other valves in the line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pressure-actuated valves which are remotelycontrolled such as by use of a solenoid to open or close a pilot valve,and more particularly relates to means to control the rate that thesevalves close.

2. Brief Description of the Prior Art

Pressure-actuated valves with which the present invention has uniqueapplication are well known in the art. They are normally comprised of adiaphragm suspended plug member with the diaphragm and plug memberforming a control chamber. When the chamber is filled with fluid theplug member is forced against its seat and the valve is closed. When thechamber is substantially empty, the plug member is positioned away fromits seat and the valve is open.

The conventional means of opening and closing the valve are a restrictedinlet port to the valve control chamber and a pilot valve which ventsthe control chamber into the low pressure side of the line. When thepilot valve is initially opened, fluid will flow from the valve chamberfaster than it enters through inlet port thereby opening the valve untilthe flow into the central chamber equalizes with the flow out of thecontrol chamber. When the pilot valve is closed, fluid flows into thecontrol chamber without flowing out thereby gradually forcing the valveplug against the valve seat.

Some of these pressure actuated valves include means to control the ratethe valve closes, mainly by means of restricting the rate of fluid flowinto the control chamber as the valve closes. If the flow into thischamber is unrestricted, the chamber will fill rapidly and the valvewill close rapidly. This rapid closing must be avoided in mostapplications because it causes a pressure shock in the fluid in theline. This pressure shock can cause the pipes to burst when they are ina weakened condition. It also causes excess wear and tear on the closingvalve as well as on other valves in the line.

If the passageway into the valve control chamber is highly restricted,the valve will close very slowly at a substantially uniform rate. Thisuniform rate is normally not necessary because the shock effect occurswhen the valve is nearly closed. Therefore a variable rate of fluid flowrestrictor is usually provided to allow the valve to close rapidly whenit is open and slower when it is nearly closed.

Attempts of providing a variable restriction to the flow of fluidthrough the inlet port have included plungers which enter the inlet portas the valve closes. The plunger substantially and abruptly reduces thecross sectional area of the inlet port thereby reducing the rate of flowinto the valve control chamber. However, an abrupt change in the closingrate of the valve is undesirable because the abrupt change itself causesundesirable transients in the line.

Other attempts of providing a variable restriction to the flow of fluidthrough the inlet port have provided the plunger within the inlet portat the time the plug begins its motion to the closed position. Variablerestriction in flow is provided by having the inlet port be a narrowpassageway which is increasingly filled by the plunger as the valvecloses. These narrow passageways are susceptible to being clogged byforeign matter in the fluid, especially in applications involvingirrigation systems where the water is "filthy" with dirt and othermaterials. These plunger/narrow passageway restrictors therefore tend tobecome inoperable over time. Consequently the valves using plungers innarrow passageways require the use of preliminary dirt filters in orderto provide a useful life for the valve.

OBJECTS AND SUMMARY OF INVENTION

It is an object of the present invention to provide a variable flowrestrictor to the valve control chamber of a pressure-actuated valvehaving a simple and easily manufactured design that provides for anexponential flow restriction, does not become clogged and does notrequire the use of a preliminary dirt filter.

It is a further object of the present invention to provide anexponentially variable flow restrictor with a self-cleaning action.

These objects are accomplished by providing a compressible spring housedin a chamber through which fluid from the supply line must flow to reachthe valve control chamber in a pressure-actuated valve. Fluid entersthis chamber exterior to the spring and exits the chamber interior tothe spring. When the valve is open, the spring's coils are spacedrelatively far apart providing the fluid relatively unrestricted accessto the valve control chamber. But as the valve closes, the coils becomeincreasingly compressed, thereby increasingly restricting the flow offluid through them into the valve control chamber to thereby slow therate the valve closes. When the valve is nearly closed, the springpresents a nearly solid wall to the flow of fluid. Therefore the valvewill slowly and gently close preventing pressure shock.

The spring resistance to the closing of the plug member is negligible inits effect on restrictive action. The flow resistance created by thecompression of the spring allows the flow restrictor to be designed withpassageways that are relatively immune from clogging by foreign matter.As the spring expands during valve opening its coils are increasinglyspaced apart to allow any accumulated foreign matter to pass through itscoils. When the spring is compressed during valve closing its coilstwist and rub together thereby providing an inherent cleaning action.

BRIEF DESCRIPTION OF THE DRAWINGS

The exact nature of the present invention will become readily apparentfrom the following detailed description when taken in conjunction withthe accompanying drawings in which:

FIG. 1 is a cross sectional view of the pressure actuated valve with thevalve parts shown in a closed position.

FIG. 2 is a fragmentary cross sectional view of the pressure-actuatedvalve isolated on the plug member and seat showing the plug member in apartially opened position.

FIG. 3 is a graph showing the relationship between valve position andits closing rate and also between valve position and the resistance tothe closure of the valve from the spring and from the flow restrictingproperties of the spring.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description is provided to enable any person of ordinaryskill in the field of pressure-actuated valves to make and use thedescribed variable flow restrictor as it is set forth herein. Theembodiment of the invention disclosed herein is the best modecontemplated by the inventor for carrying his invention into practice.

Referring first to FIG. 1, a cross sectional view of thepressure-actuated valve is disclosed. The pressure-actuated valve 10couples to a fluid supply line on its upstream side through aconventional coupling means 12 and on its downstream side throughconventional coupling means 14. When the valve is open as shown in FIG.2, fluid will flow from the supply line into chamber 16 past plug seats22 and 24 into chamber 18 and from there into the downstream supplyline.

Plug seats 22 and 24 are opposite segments of a single circularcontinuous plug seat, which shall hereinafter be referred to as plugseat 22. When plug member 20 is seated with seat 22, no fluid is free toflow from upstream chamber 16 past the plug seat 22 into downstreamchamber 18.

Plug member 20 is coupled to the body of pressure-actuated valve 10 bymeans of flexible resilient diaphragm 26. The plug member 20, diaphragm26 and the upper portion of the housing section 11 of thepressure-actuated valve 10 forms a control chamber 28. Fluid is free toflow into control chamber 28 from upstream chamber 16 through inlet port30 up passageway 32 past flow restrictor spring 34 and throughpassageway 36 into chamber 28. The inlet port, and each of thesepassageways forms a hollow ring about shaft 38, which protrudes throughplug member 20.

Fluid is free to exit from control chamber 28 through passageway 40,chamber 42, passageway 44, chamber 46 and passageway 48 into downstreamchamber 18, and from there into the downstream fluid supply line. Fluidwill flow through the series of passageways and chambers when solenoid50 withdraws its control plug 52 from seat 54. When the solenoid 50causes control plug 52 to abut against seat 54 no fluid can flow fromcontrol chamber 28 into downstream chamber 18.

When the valve 10 is closed as shown in FIG. 1, flow through passageways32 and 36 into chamber 28 is substantially blocked by flow restrictorspring 34 which is in its fully compressed position as shown. When thespring 34 is fully compressed it forms substantially a solid wall to theflow of fluid through passageway 32 and into or out of the controlchamber 28.

When solenoid 50 withdraws its control plug 52 from seat 54 it allowschamber 28 to vent fluid into upstream chamber 18. As the fluid incontrol chamber 28 vents through passageway 40, 44 and 48 intodownstream chamber 18 the pressure in control chamber 28 is reduced. Asa result, the higher pressure in chamber 16 will force plug member 20 torise off its seat 22. Diaphragm 26 will also unflex reducing the volumeof valve control chamber 28.

As this occurs fluid will begin flowing from upstream chamber 16 intodownstream chamber 18, as shown in FIG. 2. Flow restrictor spring 34will be spaced apart, as is shown in FIG. 2, allowing fluid to flowthrough the spring coils and into control chamber 28. This will allowfluid to flow into control chamber 28 from chamber 16. However becausefluid from control chamber 28 is being vented faster than it isentering, plug 20 will continue to move away from seat 22. The valve 10will continue to open. As the plug moves further away from seat 22spring 34 will become even more spaced apart allowing more fluid intochamber 28. At a certain point the flow into chamber 28 from upstreamchamber 16 will be equal to the flow venting from chamber 28 intodownstream chamber 18. At this point the valve 10 will stop opening andremain in a steady state condition.

If the solenoid 50 causes control plug 52 to seat against its seat 54closing passageway 44 from chamber 42, fluid will no longer be free tovent from valve control chamber 28 to downstream chamber 18. Pressure inthe valve control chamber 28 will then increase. The increasing fluidpressure in chamber 28 will tend to force plug member 20 toward its seat22. Thus fluid will continue to flow from upstream chamber 16 throughpassageways 32 and 36 into chamber 28 gradually forcing plug member 20towards its valve seat 22.

If the flow into chamber 28 were unrestricted, the pressure differentialbetween chamber 28 and the area just below plug member 20 would continueto increase as the flow between plug member 20 and its seat 22 continuedto become more restricted. Thus the valve would tend to increase itsclosing rate the more closed it became; and the valve would slam shutcausing a pressure shock in the fluid supply line which is otherwiseknown as hammering or chattering.

The present invention, however prevents this from happening. Flowrestrictor spring 34 is logged between passageways 32 and 36 by shoulder56 on shaft 38 and by shoulder 58 on plug member 20 so that the fluidmust flow through the coils of the spring to get from passageway 32 intopassageway 36. As the plug member closes it compresses the flowrestrictor spring 34.

As the spring 34 is compressed it tends to resist the closure of valvemember 20 with a force proportional to a constant k times thedisplacement x from an equilibrium position X_(o), which is the naturalunflexed position of the spring. This can be represented in the form ofan equation where the resistance force of the spring is equal to

    F.sub.s =-k(x-x.sub.o).

It can be seen from this equation that the resistance of the springincreases the further the valve closes and would thus tend, howevernegligably, to slow the movement of the plug member 20 toward its valveseat 22.

More important, however, is the fact that as the spring closes, the flowthrough the coils of the spring tends to become increasingly restricted.With the flow of fluid being increasingly restricted, valve controlchamber 28 will be filled at a slower rate thereby causing plug member20 to approach its seat 22 at a decreasing rate. The restriction offluid flow through the coils of spring 34 is inversely proportional tothe area through which the fluid can flow. The total area of thecylinder of the spring is given by the formula

    A=πr.sup.2 l

where r is the radius of the spring, and l is its length.

The area occupied by the spring itself is a constant C and is equal to

    C=πr.sup.2 l.sub.o

where l_(o) is the length of the spring in its fully compressedcondition. Thus at any given l, the area through which the fluid haspassageway to flow is given by the formula

    A=πr.sup.2 (l-l.sub.o).

Because the resistance to flow is inversely proportional to the areathrough which the fluid has to flow, the force of resistance F_(r) canbe written

    F.sub.r =k.sub.r /πr.sup.2 (l-l.sub.o)

where k_(r) is a constant.

This force of resistance to flow is cumulative with the force ofresistance of the spring as the spring is compressed.

A hypothetical graph of these forces is shown in FIG. 3. As can be seenfrom FIG. 3, the resistance of the spring, S--S, shown by plot 105, asit is compressed is substantially linear. The resistance to flow throughthe spring's coils, R--R, shown as plot 107, shows that the resistancesharply rises as the plug member 20 closely approaches its seat 22. Thegraph also shows a plot 109 which is the vector sum of the forces ofspring force, F_(s), and flow resistance, F_(r). Although the cumulativeresistance force, F_(t), the vector sum of F_(s) and F_(r), acts againstthe force due to the pressure differential between valve control chamber28 and the area just below plug member 20, it can be seen that the flowresistance force is the most important force. The springs actually usedtherefore may have a negligible spring constant k. Because the flowresistance force, R--R, rises sharply as the plug member 20 approachesits seat 24, the speed, C--C, of approach shown as plot 111 in FIG. 3,sharply decreases. Plug member 20 will thus softly and slowly seatagainst its seat 22. Note that instantaneous slope of any point on plot111 is proportional to the vector sum of the total resistance force,F_(t), and the force due to the pressure differential between controlchamber 28 and the area just below plug member 20.

With the plug 20 seated against its seat 22, the pressure in chambers 28and 16 will be equal. However, due to the design of the plug member 20having a broader cross sectional area on the surface 60 facing valvecontrol chamber 28 than the surface 62 facing upstream chamber 16, thecumulative force, F_(p), due to pressure on the surface 60 will begreater than the cumulative force on the surface 62, thereby holdingplug member 20 against its valve seat 22.

However, when plug member 20 is seated, spring 34 is providing a maximumforce, F_(s), tending to force the plug member off its seat 22. If thespring constant, k, of spring 34 is not sufficiently small so that thisspring force, F_(s), is not less than the force, F_(p), due to thedifference in area between plug surfaces 60 and 62, spring 34 willprevent plug member 20 from remaining seated. This difficulty can beovercome by reducing the spring constant, k, of spring 34, increasingthe area of plug surface 60 relative to plug surface 62, or providing aspring 74, lodged between housing member 11 and shoulder 76 on plugmember 20, to counterbalance the force, F_(s), of spring 34.

Such a spring 74 is provided in the preferred embodiment. This spring 74will not only assist in keeping plug member 20 seated, but it will alsoaffect the equilibrium position at which the plug member 20 is fullyopen and will aid in the closing of plug member 20 when solenoid 50shuts off the venting of fluid from control chamber 28.

Additional parts shown in FIG. 1 of the pressure-actuated valve 10 whichdo not form a part of this invention are manual controls 64 and 66. Whenmanual control 64 is operated, chamber 28 is allowed to vent to theoutside of the pressure-actuated valve 10. This allows the plug member20 to rise from its seat 22 thereby opening valve 10 to the flow offluid. When manual control 66 is operated, slide 68 is driven againstthe top 70 of plug member 20 to drive plug member 20 against its seat 22thereby closing valve 10. Chamber 72 in slide 68 will slideably receivethe upper portion of shaft 38 as slide 68 lowers into valve controlchamber 28.

It is important to note that the resistance to the closure of the plugmember 20 rises sharply in a nonlinear fashion as plug member 20approaches its seat 22. The initial movement of plug member 20 towardits valve seat can be allowed to be quite rapid. Because the rapidity ofmovement of plug member 20 toward its seat 22 is controlled by the totalcapacity of passageways 32 and 36, these passageways can be made to berelatively large as compared to devices known in the prior art whichheavily relied on a restricted bleed-type passageway to slow down theflow of fluid into the valve control chamber. The relatively large crosssectional area of the passageways 32 and 36 provides for a high dirthandling capability. Further, any dirt that does get into passageway 32cannot clog the action of flow restrictor spring 34; for when the coilsof spring 34 are fully spaced apart, any dirt lodged between the coilswill be free to flow through them and into control chamber 28.

The nonlinear flow restricting capability of the restrictor spring 34 isa surprising feature of the present invention as can be seen from thediscussion above. This not only provides a variable flow restrictor toprevent pressure shock and hammering in the supply lines, but it alsoallows the bleed-type passageways 32 and 36 to be of such a relativelylarge cross sectional area that the total capability to handle dirt andother foreign matter in the fluid entering these passageways issubstantially increased over pressure actuated valves known in the priorart. This capability is accomplished without the use of a preliminarydirt filter.

Therefore in light of the above detailed description of the preferredembodiment, I claim:
 1. In a pressure-actuated diaphragm valve having abody member, a seat mounted within said body member, a plug memberco-operable with said seat to form a valve control chamber, inlet andoutlet passageways connecting said chamber with a fluid supply line, andpilot means to cause said control chamber to fill with fluid from saidsupply line to force said plug member against said seat, the improvementtherein comprising:a hollow shaft, with an interior first shoulder, insaid plug member which allows a fluid to flow through said plug memberand into said valve control chamber; a stem having an exterior secondshoulder and having a smaller cross sectional area than said hollowshaft, said stem being mounted within said body member to protrude intosaid hollow shaft past said first shoulder; and a helical coil mountedbetween said first and second shoulders such that said coil is compactedwhen said plug member is seated against said seat and is spaced apartwhen said plug member is positioned away from said seat and said helicalcoil provides exponentially increasing resistance to the flow of fluidthrough its coils and into said valve-control chamber as said plugmember approaches said seat.